Acceleration Error – The maximum difference, at any measurand value within the specified range, between output readings taken with and without the application of acceleration.

Acceleration Error Band – The error band applicable when constant accelerations with a specified range of amplitudes are applied to a transducer along specified axes at room conditions.

Accuracy – The ratio of the error to the full–scale output (usually expressed as “within ± … percent of full scale output”) or the ratio of the error to the output, expressed in percent. Ambient Conditions – The conditions (pressure, temperature, etc.) of the medium surrounding the case of the transducer.

Ambient Pressure Error – The maximum change in output, at any measurand value within the specified range, when the ambient pressure is changed between specified values. Ambient Pressure Error Band – The error band application when the transducer operates over a specified range of ambient pressures.

Analog Output – Transducer output which is a continuous function of the measurand except as modified by the resolution of the transducer.

Attitude Error – The error due to the orientation of the transducer relative to the direction in which gravity acts upon the transducer (see Acceleration Error).

Best Straight Line – A line midway between the two parallel straight lines closest together and enclosing all output vs. measurand values after deletion of any obviously spurious data.

Breakdown Voltage Rating – The dc or sinusoidal ac voltage stated in a specification which can be applied across specified insulated portions of a transducer without causing arcing or conduction above a specified current value across the insulating material.

Burst Pressure Rating – The pressure stated in a specification which may be applied to the sensing element of a transducer without rupture of either the sensing element or transducer case as specified. (see Case Burst Pressure).

Calibration – A test during which known measurand values traceable to the NIST (National Institute of Standards and Technology) are applied to the transducer and corresponding output readings are recorded (and adjustments made if necessary).

Calibration Cycle – The application of known measurand values traceable to the NIST, and the recording of corresponding output readings, over the range of a transducer in an ascending and descending direction.

Calibration Record (or Curve) – A table or graph of the measured relationship of the transducer output to the applied measurand over the transducer range.

Case Burst Pressure – The pressure stated in a specification which may be applied to the transducer ports which may cause internal damage but will be contained within the case.

Compensation – Provision of a supplemental device or special materials to counteract known sources of error.

Dead Band – The difference between circuit closing and opening pressures at a pressure switch.

Dead Volume – The total volume of the pressure port cavity of a transducer with room barometric pressure applied.

Dithering – The application of intermittent or oscillatory acceleration forces sufficient to minimize static friction within the transducer. (This specification should not be required on modern high accuracy transducers.)

Dynamic Calibration – A calibration during which the measurand varies with time in a specified manner and the output is recorded as a function of time.

End Points – The outputs at the specified upper and lower limits of the range.

Environmental Conditions – Specified external conditions (shock, vibration, temperature, etc.) to which a transducer may be exposed during shipping, storage, handling, and operation.

Error – The algebraic difference between the indicated value and the true value of the measurand, usually expressed in percent of the full scale output, sometimes expressed in percent of the output reading of the transducer.

Error Band – The band of allowable deviations of output values from a specified reference line or curve due to those causes attributable to the transducer, as measured over two consecutive calibration cycles unless otherwise specified.

Error Curve – A graphical representation of errors obtained from a specified number of calibration cycles.

Excitation – The external electrical voltage and/or current applied to a transducer for its proper operation.

FDR/AIDS – Flight Data Recorder/Airborne Integrated Data System.

Frequency Response – The change with frequency of the output/ measurand amplitude ratio (and of the phase difference between output and measurand) for a sinusoidally varying measurand applied to a transducer within a stated range of measurand frequencies, usually specified as “within ± … percent from … to … Hz”.

Friction Error – The maximum change in output, at any measurand value within the specified range, before and after minimizing friction within the transducer.

Friction–Free Calibration – Calibration under conditions minimizing the effect of static friction, obtained by dithering. (Dithering should not be required on modern high accuracy transducers).

Full–Scale Output – The algebraic difference between the end points.

Hysteresis – The maximum difference in output, at any given measurand value within the specified range, when the value is approached first with increasing and then with decreasing measurand.

Input Impedance – The impedance (presented to the excitation source) measured across the excitation terminals of a transducer.

Insulation Resistance – The resistance measured between specified insulated portions of a transducer when a specified dc voltage is applied at room conditions unless otherwise stated.

Life, Cycling – The specified minimum number of full range excursions or specified partial range excursions over which a transducer will operate as specified without changing its performance beyond specified tolerances.

Life, Storage – The specified minimum length of time over which a transducer can be exposed to specified environmental (storage) conditions without changing its performance beyond specified tolerances.

Linearity – The closeness of a calibration curve to a specified straight line.

Linearity, End Point – Linearity referred to a straight line between the end points.

Linearity, Independent – Linearity referred to the best straight line.

Linearity, Least Squares – Linearity referred to a straight line for which the sum of the squares of the residuals is minimized.

Load Impedance – The impedance presented to the output terminals of a transducer by the associated external circuitry.

Loading Error – An error due to the effect of the load impedance on the transducer output.

Measurand – A physical quantity, property or condition which is measured.

Measured Fluid – The fluid which comes in contact with the sensing element.

Mounting Error – The error resulting from mechanical deformation of the transducer caused by mounting the transducer and making all measurand and electrical connections.

Output – The electrical quantity, produced by a transducer, which is a function of the applied measurand.

Output Impedance – The internal impedance of the transducer present at the output terminals.

Overload – The maximum magnitude of measurand that can be applied to a transducer without causing a change in performance beyond specified tolerance.

Overshoot – In an underdamped transducer, the amount of output measured beyond the final steady output value in response to a step change in the measurand.

Pressure, Line – The maximum fluid pressure the transducer will tolerate at the pressure point without affecting its calibration. Pressure Transducers:

Absolute – Measures the working fluid pressure difference from perfect vacuum.

Gauge – Measures the difference of the working fluid pressure and the ambient pressure where the transducer is located.

Differential – Measures the difference of the pressures of the fluids at the reference and pressure ports of the transducer. Two types of differential transducers are: unidirectional (PSIUD) which measures a single polarity working fluid pressure with respect to the referenced port, and bidirectional (PSIBD) which can measure plus/minus with respect to the fluid pressure at the reference port of the transducer.

Sealed – Measures the working pressure with respect to the pressure chosen by the transducer manufacturer to seal the reference side of the transducer (the sealed pressure is usually the atmospheric pressure of the transducer manufacturer’s facility).

Pressure Units – Six units of pressure are in common use:

• Standard atmosphere Pounds per square inch (psi)
• Inches of mercury ( ''Hg)
• Kilo Pascal (kPa)
• Inches of water (''H₂O)
• Torr, mm of mercury (mm–Hg)

Proof Pressure – The maximum pressure which may be applied to the sensing element of a transducer without changing the transducer performance beyond specified tolerances.

Random Errors – Relatively inconstant errors caused by measurement noise; usually expressed as a quantity indicating uncertainty limits using statistical terms.

Random Vibration – Non–periodic vibration, described only in statistical terms, most commonly taken to mean vibration characterized by an amplitude distribution which essentially follows the normal error curve (Gaussian distribution).

Range – The spectrum of measurand values, over which a transducer is intended to measure, specified by upper and lower limits.

Recovery Time – The time interval, after a specified overload, after which a transducer again performs within its specified tolerances.

Reference Pressure – The pressure or the range of pressures relative to which a differential pressure transducer measures pressure difference and which can be applied without changing the transducer’s performance beyond specified tolerances.

Repeatability – The ability of a transducer to reproduce output readings within a specified tolerance when the same measurand value is applied to it repeatedly, under the same conditions, and in the same direction.

Resolution – The magnitude of output step changes (expressed in percent of full scale output) as the measurand is continuously varied over the range.

Resonances – Amplified vibrations of transducer components, within narrow frequency bands, as vibration in specified transducer axes.

Response Time – The length of time required for the output of a transducer to rise to a specified percentage of its final value as a result of a step change of measurand.

Ripple – The r m s ac component of a transducer’s dc output voltage expressed in percent of the average value of the total output voltage.

Rise Time – The length of time for the output of a transducer to rise from a small to a large specified percentage of its final value.

Room Conditions – Ambient environmental conditions for conducting operational tests which have been established as follows:

a. Temperature: 25°±10°C (77°±18°F)

b. Relative humidity: 90% or less

c. Barometric pressure: 26 to 32 inches of mercury

Self Heating – Internal heating resulting from electrical energy dissipated within the transducer.

Sensing Element – That part of the transducer which responds directly to the measurand.

Sensitivity – The ratio of the change in transducer output to a change in the value of the measurand.

Sensitivity Shift – A change in the slope of the calibration curve.

Span – The algebraic difference between the limits of the range.

Stability – The ability of a transducer to retain its performance throughout its specified operating life and storage life.

Static Calibration – A calibration performed under room conditions by application of the measurand to the transducer in discrete amplitude intervals.

Static Error Band – The error band applicable at room conditions and in the absence of any vibration, shock, or acceleration.

Static Pressure – The force per unit area acting on a wall by a fluid at rest or flowing parallel to the wall in a pipeline.

Strain Error – The error resulting from a strain imposed on a surface to which the transducer is mounted.

Systematic Errors – Relatively constant errors caused by effects such as sensitivity shift, zero shift and known nonlinearities.

Temperature Error – The maximum change in output at any measurand value within the specified range, when the transducer temperature is changed from room temperature to specified temperature extremes.

Temperature Error Band – The error band applicable over stated environmental temperature limits.

Temperature Gradient Error – The transient deviation in output of a transducer at a given measurand value when the ambient temperature of the measurand temperature changes at a specified rate between specified magnitudes.

Theoretical Curve – The specified relationship (table, graph, or equation) of the transducer output to the applied measurand over the range.

Theoretical End Points – The specified points between which the theoretical curve is established and to which no end point tolerances apply.

Threshold – The smallest change in the measurand that will result in a measurable change in transducer output.

Time Constant – The length of time required for the output of a transducer to rise to 63% of its final value as a result of a step change of measurand.

Traceability – The relationship of a transducer calibration, through a step–by–step process, to an instrument or group of instruments calibrated and certified by the National Institute of Standards and Technology.

Transducer – A device which provides a usable output in response to a specified measurand.

Vibration Error – The maximum change in output, at any measurand value within the specified range, when vibration levels of specified amplitude and range of frequencies are applied to the transducer along specified axes at room conditions.

Vibration Error Band – The error band applicable when vibration levels with a specified range of frequencies and amplitudes are applied to a transducer along specified axes at room conditions.

Wet/Dry Differential Transducer – Wetted part (where the fluid is applied) is isolated from the internal circuitry. The circuitry is exposed to the fluid in the dry port.

Wet/Wet Differential Transducer – Reference and pressure ports are isolated from the internal circuitry.

Wetted Parts – All internal parts which are exposed to the measured fluid.

Zero Shift – An error characterized by a parallel displacement of the entire calibration curve.

References
Boeing:
D6–13450 Qualification Tests for Boeing Designed 747 Electrical/Electronic Equipment
D6–25382–14 Transducer Design Guide
BDM–1622 Hydraulic Systems
BACD2036 Boss, Recessed Seal – Standard Dimensions for MS33649 Bosses Fluid Connection Internal Straight Thread BACC45FS Connector, Electrical, Plug, Straight, Threaded Coupling
Industry:
ISA–S37.1 Standards and Practices for Instrumentation, Electrical Transducer Nomenclature and Terminology
RTCA/D0–160 Radio Technical Commission for Aeronautics/ Environmental Conditions and Test Procedures for Airborne Equipment
Military:
MIL–F–18180 Flanges and Flanged Fittings, General Specification